Is it okay to apply voltage to pins before turning on MCU power supply?

Question:

Is it okay to apply voltage to the pins before turning on the MCU power supply (VCC = 0 [V])?

Answer:

When VCC = 0, do not apply any voltage higher than VCC to the signal pins of ports.
Doing so would cause current to flow through the pin protection diode and also cause the input voltage (VIN) to exceed the absolute maximum rating for guaranteed MCU operation (VCC + 0.3 V), which in a worse case scenario may destroy the device.